1. Field of the Invention
The present invention relates to spinal fusion, and in particular to a device enhancing bone fusion.
2. Description of the Related Art
When the human spinal column is subjected to force or extreme angles, discs between adjacent vertebrae can experience long-term compression, whereby soft tissues of the discs retrograde or protrude from the spinal column. The protruded soft tissues of the disc press nerves, causing pain.
To solve the aforementioned problem, the disc is conventionally removed. A bone graft is then implanted in the gap vacated by the disc, fusing the adjacent vertebrae. The spinal column is thus fixed and stabilized. Moreover, to guarantee bone fusion and prevent the bone graft from breakage and separation from the vertebrae due to insufficient strength thereof, an internal cage is often applied with the bone graft. In order to bear high compression or stress from the vertebrae in different positions, the internal cage is often metal (such as stainless steel or titanium alloy) or macromolecular material (such as Polyetheretherketone, PEEK).
In addition to supporting the adjacent vertebrae, the internal cage guides newgrown bone proliferating from adjacent vertebrae thereinto, thereby enabling bone fusion. Specifically, the internal cage has a hollow interior to receive the bone graft, which induces the bone fusion. Additionally, to reduce complexity of surgery and hospital time, the internal cage combines artificial porous bone material to induce proliferation of bone.
U.S. Pat. No. 6,245,108 discloses a prosthetic implant comprising a hollow casing with a plurality of ridges formed thereon. The ridges enhance engagement between the prosthetic implant and adjacent vertebrae, such that the prosthetic implant can be secured therebetween. The hollow casing receives a bone graft. Nevertheless, fragments of the bone graft easily pass out of the hollow casing, increasing the difficulty of implantation.
U.S. Pat. No. 5,609,635 discloses an interbody spinal fusion implant configured with an upper plate and a lower plate. A bone graft is contained in the interbody spinal fusion implant and maintained between the upper plate and the lower plate, preventing fragments from escaping during implantation surgery.
U.S. Pat. No. 5,865,848 discloses a spinal fusion implant assembly with a detachable structure receiving a bone graft. Multiple complementary protrusions and recesses are formed on a-top surface and a bottom surface, enhancing engagement between the spinal fusion implant assembly and adjacent vertebrae.
WO2005/037137A2 discloses a spinal cage with a hollow interior receiving a bone graft. The spinal cage is integrally formed and can be easily implanted between two adjacent vertebrae.
Accordingly, the bone graft (including both organic and artificial bone) is accommodated in the interior of the prosthetic implant, interbody spinal fusion implant, spinal fusion implant assembly, or spinal cage. Bone proliferates along the interior of the prosthetic implant, interbody spinal fusion implant, spinal fusion implant assembly, or spinal cage and then covers the exterior thereof. The prosthetic implant, interbody spinal fusion implant, spinal fusion implant assembly, or spinal cage, however, is composed of metal or macromolecular material which provides poor bone guidance and bonding. New bone covers the exterior of the prosthetic implant, interbody spinal fusion implant, spinal fusion implant assembly, or spinal cage after fibered connective tissues are formed thereon. Thus, loose bone bonding with the prosthetic implant, interbody spinal fusion implant, spinal fusion implant assembly, or spinal cage and poor bone fusion are easily generated.
Hence, there is a need for a spinal fusion device receiving a bone graft. The spinal fusion device bears compression or stress from adjacent vertebrae and enables newgrown bone from the vertebrae to simultaneously grow along the interior and exterior of the spinal fusion device and fuse with the bone graft.